(1) Field of the Invention
The present invention relates to a process for the manufacture of a gel capsule loaded with at least one organic percarboxylic acid, as well as the gel capsules manufactured in this manner. Furthermore, the present invention relates to the use of these gel capsules as bleaching agents or components of bleaching agents, particularly for their use in washing and cleaning agents, particularly in liquid washing and cleaning agents, tooth-care products, hair colorants and decolorizing or bleaching agent compositions for technical uses, as well as the products comprising these gel capsules, i.e. washing and cleaning agents, particularly liquid washing and cleaning agents, tooth-care products, hair colorants and decolorizing or bleaching agent compositions for technical uses, which comprise the inventive gel capsules.
For liquid, particularly aqueous washing and cleaning agents that are enjoying an increased popularity due to their positive product properties, such as a better and faster solubility and practicality, the addition to the formulation or incorporation of bleaching (agent) components is problematic for numerous reasons. Due to their decomposition reactions or hydrolysis and incompatibilities towards other constituents of the washing agent formulation, such as, e.g., enzymes or surfactants, the added bleaching agents often lose their activity already on storage or even during product utilization. An adverse consequence resulting from this, is that the washing performance—particularly the bleaching power—of the washing agent formulation noticeably deteriorates, such that bleachable stains in particular can no longer be satisfactorily removed.
Bleaching agents, such as for example perborates or percarbonates, which are usually used in solid washing agent formulations, are extremely moisture sensitive, with the result that they often lose their bleaching power within a few days in a liquid and particularly aqueous washing or cleaning agents, due to the loss of active oxygen.
On the other hand, percarboxylic acids, especially imidopercarboxylic acids, the most important representative of which is phthalimidopercapric acid (PAP), are more efficient and less sensitive to hydrolysis and are known in the prior art as bleaching agents for washing and cleaning agents. Nevertheless, their storage stability is by far insufficient to guarantee a long-term use of the corresponding washing and cleaning agent without the consequent loss in activity. The addition of percarboxylic acids, particularly imidopercarboxylic acids, in liquid washing and cleaning agents is therefore particularly problematic.
Because of the disadvantages that result from a modification of the washing and cleaning agent formulation as a consequence of the decomposition of imidopercarboxylic acids, particularly PAP, attempts have been made in the prior art to efficiently encapsulate the imidopercarboxylic acids (e.g., PAP), such that the imidopercarboxylic acid cannot come into contact with the rest of the components of the washing or cleaning agents.
(2) Description of Related Art, Including Information Disclosed Under 37 C.F.R. §§ 1.97 and 1.98
Thus, EP 0 510 761 B1 or U.S. Pat. No. 5,230,822, which belongs to the same patent family, describes a process for encapsulating washing agent additives in general, such as enzymes, bleaching agents, comprising inter alia PAP, bleaching agent precursors and bleach catalysts, wherein a wax with a melting point between 40° C. and 50° C. is used as the protective shell for the encapsulation. The coated washing particle is manufactured by spraying molten wax onto the particles. For this, the wax must first be heated to temperatures above its melting point; this can sometimes be deleterious for the substances being encapsulated. This process has also the disadvantage that the active substance will be released only at temperatures above the melting point of the applied wax—therefore only above temperatures between 40° C. and 50° C. This particularly falls short of the requirements of today's consumer or user, as—bearing in mind the development of higher performance washing and cleaning agent formulations and the saving in energy costs—washing should also be often carried out at lower temperatures, particularly at about 30° C. Moreover, a wax with a high melting point has the disadvantage that, particularly at low temperatures, it leaves residues on the washing, as it is not completely emulsified at these temperatures.
EP 0 653 485 A1 relates to capsule compositions of active substances that can comprise, inter alia, bleaching agents, such as PAP, and in which the active substance inside the capsule is present as a dispersion in oil. The manufacture of these capsules, whose shell is formed of polymers that only dissolve during the washing process or the application, necessitates an expensive and technologically non-trivial operation of an emulsification process.
WO 03/045545 A1 describes capsules that contain active substances and which are produced by means of a mini emulsion process using a carrier phase and a block copolymer. The mentioned active substances have to be dissolved in the oil phase, with the result that the described capsule systems are largely restricted to active substances soluble in the oil phase, particularly hydrophobic active substances. Bleaching agents are not mentioned here. A high-pressure homogenization is required to manufacture the mini emulsion.